Relay system and switching device

ABSTRACT

When relaying a frame received at a MCLAG port to a bridge port, a MCLAG identifier adding unit adds a MCLAG identifier to the frame. When an encapsulated frame to which a MCLAG identifier has been added is received at the bridge port and the encapsulation of the frame, is performed by a peer device, a learning information control unit does not learn an encapsulation address contained in the encapsulated frame. More specifically, the learning information control unit learns a source customer address contained in the frame in association with the MCLAG identifier added to the frame to the address table, but does not learn a source encapsulation address.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent ApplicationNo. 2014-223504 filed on Oct. 31, 2014, the content of which is herebyincorporated by reference into this application.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a relay system and a switching device,for example, a relay system in which a link aggregation group is setacross two switching devices to perform an operation based on PBB(Provider Backbone Bridge) standard and the switching device.

BACKGROUND OF THE INVENTION

Japanese Patent Application Laid-Open Publication No. 2012-161027(Patent Document 1) discloses a configuration in which a node redundancyis applied to two edge switching devices disposed at the boundary of aMAC-in-MAC network. In this document, when MAC addresses of one deviceand the other device are defined as a my representative address and amate representative address, respectively, each of two edge switchingdevices controls a stream of frames based on the combination of the myrepresentative address and the mate representative address contained ina destination and a source of a frame. For example, when an encapsulatedframe destined for a my representative address is received from a coreswitch and a destination customer address has not been learned, one ofthe two edge switching devices decapsulates the encapsulated frame andthen relays it to an access port, and further relays the encapsulatedframe to the other device via an IC port. Then, the other device alsodecapsulates the received encapsulated frame and then relays it to anaccess port.

Japanese Patent Application Laid-Open Publication No. 2012-209984(Patent Document 2) discloses a configuration in which an inter-devicelink aggregation is set on each link between a customer edge in a usernetwork and two provider edges in a MPLS network. When the two provideredges receive a packet from the customer edge, only one of the twoprovider edges relays the packet to the MPLS network based on a rulemade in advance between the two provider edges.

SUMMARY OF THE INVENTION

As a redundant system, for example, a system in which two switchingdevices are connected to each other via bridge ports and a LAG is set ona plurality of ports including respective ports of the two switchingdevices as described in Patent Document 2 has been known. In thisredundant system, unlike a common LAG set in one switching device, a LAGis set across two switching devices. Therefore, in addition to generaleffects obtained by the LAG such as the redundancy for the fault ofcommunication lines and the expansion of communication band, theredundancy for the fault of switching devices can be achieved.

In this specification, the inter-device LAG as described above isreferred to as a multi-chassis link aggregation group (hereinafter,abbreviated as MCLAG). Also, the assembly of the two switching deviceson which MCLAG is set is referred to as MCLAG switch. Further, whenviewed from one switching device of two switching devices, the otherswitching device is referred to as a peer device.

The MCLAG switch manages the inter-device ports, on which the same MCLAGis set, as logically one port. As one method for realizing it, when eachof the two switching devices constituting the MCLAG switch relays aframe received at the port, on which MCLAG is set (hereinafter, referredto as MCLAG port), to the peer device via the bridge port, the switchingdevice adds an identifier of the MCLAG to the frame. The peer devicelearns a source MAC address of the frame received at the bridge port inassociation with the identifier of the MCLAG to its own address table.

Further, as a technique for realizing a wide-area Ethernet, for example,the extended VLAN and the MAC-in-MAC have been known as described inPatent Document 1. The extended VLAN is standardized by IEEE 802.1ad,and is a technique for extending the number of VLANs (Virtual Local AreaNetwork) by adding a service-provider VLAN tag to a customer VLAN tagbased on IEEE 802.1Q. The MAC-in-MAC is a technique of encapsulating acustomer MAC (Media Access Control) frame by a service-provider MACframe, thereby achieving the further extension of the number of VLANsbased on the extended VLAN and the reduction of the number of MACaddresses learned in a switch (core switch) in a wide-area network. As adetailed method of the MAC-in-MAC, PBB based on IEEE 802.1ah has beenknown.

Here, the inventors of the present invention have studied theapplication of the MCLAG switch to the edge switching device of the PBBnetwork. In this case, the MCLAG switch can receive a frame from acustomer network at any of the MCLAG ports of the two switching devices.Thus, each of the two switching devices receives a frame at its ownMCLAG port or receives a frame received at the MCLAG port of the peerdevice at its own bridge port.

In the former case, the frame received at the MCLAG port is anunencapsulated frame, and in the latter case, the frame received at thebridge port may be an encapsulated frame as described in PatentDocument 1. Thus, there are the case where the learning of the addresstable is executed based on an unencapsulated frame and the case where itis executed based on an encapsulated frame. Generally, the learningcontents of the address table differ between the unencapsulated frameand the encapsulated frame. As a result, the situation may occur inwhich the learning contents of the address table are unnecessarilychanged in spite of being intended for the same terminal or the like.

The present invention has been made in view of the problem mentionedabove, and one object of the present invention is to provide a relaysystem and a switching device capable of preventing the unnecessarychange of the learning contents of an address table.

The above and other objects and novel characteristics of the presentinvention will be apparent from the description of the presentspecification and the accompanying drawings.

The following is a brief description of an outline of the typicalembodiment of the invention disclosed in the present application.

A relay system according to an embodiment of the present inventionincludes: a first switching device and a second switching device whichare disposed at entrance or exit of a PBB network in which relayingbased on a PBB standard is performed. Each of the first and secondswitching devices converts an unencapsulated frame received from outsideof the PBB network into an encapsulated frame and relays theencapsulated frame to the PBB network, and converts the encapsulatedframe received from the PBB network into the unencapsulated frame andrelays the unencapsulated frame to the outside of the PBB network. Theunencapsulated frame contains a customer address, and the encapsulatedframe has a configuration in which an encapsulation address is added tothe unencapsulated frame based on the PBB standard. Each of the firstswitching device and the second switching device includes: a lower-linkport; an upper-link port; one or a plurality of MCLAG ports; a bridgeport; an address table; and a relay processing unit which learns andretrieves the address table. The lower-link port transmits or receivesthe unencapsulated frame, and the upper-link port transmits or receivesthe encapsulated frame. An inter-device LAG is set on the one or aplurality of MCLAG ports, and the one or a plurality of MCLAG portsinclude a first MCLAG port serving as the lower-link port. The bridgeport serves as the upper-link port and connects one device and a peerdevice. The address table retains the customer address present ahead ofthe lower-link port in association with a port identifier representingthe lower-link port or a MCLAG identifier corresponding to thelower-link port. Also, the address table retains the customer addresspresent ahead of the upper-link port in association with theencapsulation address and a port identifier representing the upper-linkport or a MCLAG identifier corresponding to the upper-link port. Therelay processing unit includes: a MCLAG identifier adding unit and alearning information control unit. When a frame received at the MCLAGport is relayed to the bridge port, the MCLAG identifier adding unitadds a MCLAG identifier corresponding to the MCLAG port to the frame.When the encapsulated frame to which the MCLAG identifier has been addedis received at the bridge port and encapsulation of the frame isperformed by the peer device, the learning information control unitlearns a source customer address contained in the encapsulated frame inassociation with the MCLAG identifier added to the encapsulated frame tothe address table. At this time, the learning information control unitdoes not learn the encapsulation address contained in the encapsulatedframe to the address table.

The effects obtained by typical embodiments of the invention disclosedin the present application will be briefly described below. That is, ina relay system including a MCLAG switch, it is possible to prevent theunnecessary change of the learning contents of an address table.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an overall configuration exampleand an operation example of a relay system according to an embodiment ofthe present invention;

FIG. 2 is a diagram showing a configuration example of a main part of aframe flowing in each relay network in the relay system of FIG. 1;

FIG. 3 is a schematic diagram showing a configuration example around theMCLAG switch in the relay system of FIG. 1;

FIG. 4 is an explanatory diagram showing an operation example of therelay system of FIG. 3;

FIG. 5 is an explanatory diagram showing another operation example ofthe relay system of FIG. 3;

FIG. 6 is a block diagram showing a configuration example of the mainpart of the switching device constituting the MCLAG switch in the relaysystem of FIG. 3;

FIG. 7 is a schematic diagram showing a configuration example of theaddress table in FIG. 6;

FIG. 8A is a schematic diagram showing a configuration example of areception-side IVID management table in FIG. 6;

FIG. 8B is a schematic diagram showing a configuration example of atransmission-side IVID management table in FIG. 6;

FIG. 8C is a schematic diagram showing a configuration example of aMCLAG table in FIG. 6; and

FIG. 9 is an explanatory diagram showing an operation example in thecase where the relay system of FIG. 3 does not have a learninginformation control unit in the relay system studied as a premise of thepresent invention.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

In the embodiments described below, the invention will be described in aplurality of sections or embodiments when required as a matter ofconvenience. However, these sections or embodiments are not irrelevantto each other unless otherwise stated, and the one relates to the entireor a part of the other as a modification example, details, or asupplementary explanation thereof. Also, in the embodiments describedbelow, when referring to the number of elements (including number ofpieces, values, amount, range, and the like), the number of the elementsis not limited to a specific number unless otherwise stated or exceptthe case where the number is apparently limited to a specific number inprinciple, and the number larger or smaller than the specified number isalso applicable.

Further, in the embodiments described below, it goes without saying thatthe components (including element steps) are not always indispensableunless otherwise stated or except the case where the components areapparently indispensable in principle. Similarly, in the embodimentsdescribed below, when the shape of the components, positional relationthereof, and the like are mentioned, the substantially approximate andsimilar shapes and the like are included therein unless otherwise statedor except the case where it is conceivable that they are apparentlyexcluded in principle. The same goes for the numerical value and therange described above.

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. Note that componentshaving the same function are denoted by the same reference charactersthroughout the drawings for describing the embodiments, and therepetitive description thereof will be omitted.

<<Overall Configuration of Relay System>>

FIG. 1 is a schematic diagram showing an overall configuration exampleand an operation example of a relay system according to an embodiment ofthe present invention. The relay system shown in FIG. 1 includes aplurality of (in this case, six) customer networks 12 a to 12 f, aplurality of (in this case, three) PB networks 11 a to 11 c for relayingbetween the customer networks 12 a to 12 f and a PBB network 10 forrelaying between the PB networks 11 a to 11 c.

The PB network 11 a handles relaying between the customer networks 12 aand 12 b, the PB network 11 b handles relaying between the customernetworks 12 c and 12 d, and the PB network 11 c handles relaying betweenthe customer networks 12 e and 12 f. The PBB network 10 is a relaynetwork in which relaying based on IEEE802.1ah (in other words, PBBstandard) is executed. The PB networks 11 a to 11 c are relay networksto which the above-described extended VLAN is applied.

Switches SWB1 and SWB2 are disposed at boundaries between the customernetworks 12 a and 12 b and the PB network 11 a, respectively. Thecustomer network 12 a includes a plurality of customer terminals TM anda network NWc1 which connects the customer terminals TM to the switchSWB1. The customer network 12 b includes a plurality of customerterminals TM and a network NWc2 which connects the customer terminals TMto the switch SWB2. Each of the networks NWc1 and NWc2 is made up of,for example, communication lines and switches (not shown). The switchSWB1 handles relaying between the plurality of customer terminals TM inthe customer network 12 a and handles also relaying between eachcustomer terminal TM and the PB network 11 a. The switch SWB2 handlesrelaying between the plurality of customer terminals TM in the customernetwork 12 b and handles also relaying between each customer terminal TMand the PB network 11 a.

Similarly, switches SWB3 and SWB4 are disposed at boundaries between thecustomer networks 12 c and 12 d and the PB network 11 b, respectively,and switches SWB5 and SWB6 are disposed at boundaries between thecustomer networks 12 e and 12 f and the PB network 11 c, respectively.The customer networks 12 c to 12 f each include a plurality of customerterminals TM and networks NWc3 to NWc6, respectively. The switches SWB3and SWB4 handle relaying between the plurality of customer terminals TMin the customer networks 12 c and 12 d and handle also relaying betweeneach customer terminal TM and the PB network 11 b. The switches SWB5 andSWB6 handle relaying between the plurality of customer terminals TM inthe customer networks 12 e and 12 f and handle also relaying betweeneach customer terminal TM and the PB network 11 c.

At the boundary between the PB network 11 b and the PBB network 10 (inother words, entrance or exit of PBB network 10), a switching device(specifically, edge switching device) SWE2 is disposed. The switchingdevice SWE2 has a plurality of ports including n ports Pd[1] to Pd[n]serving as lower-link ports and a port Pu serving as an upper-link port.The PB network 11 b is provided with a network NWb2 made up of, forexample, communication lines and switches (not shown). The switches SWB3and SWB4 are connected to any of the ports Pd[1] to Pd[n] of theswitching device SWE2 through the network NWb2.

Thus, the switching device SWE2 handles relaying between the pluralityof switches SWB3 and SWB4 present in its own lower link and handles alsorelaying between each of the switches SWB3 and SWB4 and the PBB network10. Although the two switches SWB3 and SWB4 are disposed at the boundaryof the PB network 11 b in this case, more switches are disposed inpractice. Also, in accordance with this, more customer networks areincorporated in the PB network 11 b in addition to the two customernetworks 12 c and 12 d. The same is true for the PB networks 11 a and 11c.

Like the case of the PB network 11 b, a switching device SWE3 isdisposed at the boundary between the PB network 11 c and the PBB network10. The PB network 11 c is provided with a network NWb3. The switchesSWB5 and SWB6 are connected to any of the ports Pd[1] to Pd[n] of theswitching device SWE3 through the network NWb3. Thus, the switchingdevice SWE3 handles relaying between the plurality of switches SWB5 andSWB6 present in its own lower link and handles also relaying betweeneach of the switches SWB5 and SWB6 and the PBB network 10. Furthermore,a switching device SWE4 is disposed at the boundary between apredetermined PB network (not shown) and the PBB network 10 in the samemanner.

Meanwhile, at the boundary between the PB network 11 a and the PBBnetwork 10 (in other words, entrance or exit of PBB network 10), a MCLAGswitch MCLAGSW made up of two switching devices (edge switching devices)SWE1 a and SWE1 b is disposed. Each of the switching devices SWE1 a andSWE1 b has lower-link ports and upper-link ports. In this example, thelower-link ports include a MCLAG port Pm1 and a port Pd on which MCLAGis not set. Also, the upper-link ports include a MCLAG port Pm2, a portPu on which MCLAG is not set and a bridge port Pb.

Each of the switching devices SWE1 a and SWE1 b sets a common MCLAG1 onits own MCLAG port Pm1 and the MCLAG port Pm1 of a peer device, and setsa common MCLAG2 on its own MCLAG port Pm2 and the MCLAG port Pm2 of apeer device. The PB network 11 a is provided with a network NWb1. Theswitches SWB1 and SWB2 are connected to any of the plurality oflower-link ports of the MCLAG switch MCLAGSW through the network NWb1.Thus, the MCLAG switch MCLAGSW handles relaying between the plurality ofswitches SWB1 and SWB2 present in its own lower link and handles alsorelaying between each of the switches SWB1 and SWB2 and the PBB network10.

The PBB network 10 is provided with a network NWbb made up of, forexample, communication lines and switches (specifically, core switches(not shown)). The upper-link ports (ports Pu) of the plurality ofswitching devices SWE2 to SWE4 and the upper-link ports (port Pu andMCLAG port Pm2) of the MCLAG switch MCLAGSW are connected to each otherthrough the network NWbb. Although the case in which one of edgeswitching devices is made up of the MCLAG switch MCLAGSW has beendescribed as an example, the other edge switching devices SWE2 to SWE4may be made up of MCLAG switches.

<<Overall Operation of Relay System>>

Here, an operation example of the relay system of FIG. 1 will bedescribed based the case where a frame is transferred from the customerterminal TM in the customer network 12 c to the customer terminal TM inthe customer network 12 e in FIG. 1. In this case, a MAC address(customer address) CMAC of the customer terminal TM in the customernetwork 12 c serving as a transmission source is “CA21” and a MACaddress (customer address) CMAC of the customer terminal TM in thecustomer network 12 e serving as a destination is “CA31”. Also, a MACaddress (encapsulation address) BMAC of the switching device SWE2 is“BA2” and a MAC address (encapsulation address) BMAC of the switchingdevice SWE3 is “BA3”.

FIG. 2 is a diagram showing a configuration example of a main part of aframe flowing in each relay network in the relay system of FIG. 1. Asshown in FIG. 1 and FIG. 2, the source customer terminal TM firsttransmits a frame FL1 into the customer network 12 c. The frame FL1 inthe customer network 12 c is an unencapsulated frame containing acustomer VLAN tag 15, a source customer address CMAC (CSA) and adestination customer address CMAC (CDA). In this case, the sourcecustomer address CSA is the MAC address “CA21” and the destinationcustomer address CDA is the MAC address “CA31”. The customer VLAN tag 15contains a customer VLAN identifier CVID arbitrarily set by a customer.

Next, as shown in FIG. 1, the switch SWB3 receives the frame FL1 andtransmits a frame FL2 into the PB network 11 b. The frame FL2 is anextended VLAN frame and is an unencapsulated frame obtained by adding aservice VLAN tag 16 to the frame FL1 as shown in FIG. 2. The serviceVLAN (extended VLAN) tag 16 contains a service VLAN identifier SVIDarbitrarily set by a service provider or the like. A broadcast domain inthe PB network 11 b is determined by the service VLAN identifier SVID.The switch SWB3 adds the service VLAN tag 16 to the frame FL1 based onthe setting of the service provider or the like.

Subsequently, as shown in FIG. 1, the edge switch SWE2 receives theframe FL2 and transmits a frame FL3 into the PBB network 10. The frameFL3 is a PBB frame and is an encapsulated frame. The encapsulated framegenerally has a configuration in which an encapsulation address is addedto an unencapsulated frame based on the PBB standard. Specifically, asshown in FIG. 2, the frame FL3 has a configuration obtained byencapsulating the frame FL2 with a service instance identifier ISID, abackbone VLAN tag (B tag) 18, a source encapsulation address BMAC (BSA)and a destination encapsulation address BMAC (BDA).

The service instance identifier ISID is contained in a service instancetag (I tag) 17 with the inclusion of the above-mentioned source customeraddress CSA and destination customer address CDA. The service instanceidentifier ISID is an identifier for identifying a customer and has a24-bit region. This 24-bit region makes it possible to further extend a12-bit service VLAN identifier SVID. The service instance identifierISID is arbitrarily set by a service provider or the like. As a typicalsetting method, for example, a method of associating one service VLANidentifier SVID with one service instance identifier ISID or a method ofassociating a plurality of service VLAN identifiers SVID with oneservice instance identifier ISID has been known.

The backbone VLAN tag (B tag) 18 contains a backbone VLAN identifierBVID. The backbone VLAN identifier BVID is an identifier for controllingrelay paths and has a 12-bit region. The broadcast domain in the PBB 10is determined by the backbone VLAN identifier BVID. The backbone VLANidentifier BVID is set by a service provider or the like. As a typicalsetting method, for example, a method of associating a plurality ofservice instance identifiers ISID with one backbone VLAN identifier BVIDhas been known.

Here, as shown by the address table FDB of FIG. 1, it is presupposedthat the switching device SWE2 has learned the correspondence relationamong the customer address CMAC “CA31”, the encapsulation address BMAC“BA3” and the port identifier {Pu} of the port Pu through pastcommunications. In this specification, for example, {AA} represents anidentifier (ID) for “AA”. Also, in the address table FDB, thecorrespondence relation between the customer address CMAC “CA21” and theport identifier {Pd[1] } is also learned from the source informationupon reception of the frame FL2.

The switching device SWE2 encapsulates the frame FL2 based on “CA31” ofthe address table FDB so that its own MAC address “BA2” is contained asthe source encapsulation address BSA and the MAC address “BA3” of theswitching device SWE3 is contained as the destination encapsulationaddress BDA as shown by the frame FL3 of FIG. 2. Then, the switchingdevice SWE2 transmits the frame FL3 serving as an encapsulated framefrom the port (upper-link port) Pu to the switching device SWE3.

The switching device SWE3 receives the frame FL3 and learns thecorrespondence relation among the source customer address CSA “CA21”,the source encapsulation address BSA “BA2” and the port identifier {Pu}to the address table as shown in FIG. 1. Also, since the destinationencapsulation address BDA “BA3” of the frame FL3 is directed to theswitching device SWE3 itself, the switching device SWE3 retrieves theaddress table FDB with using the destination customer address CDA “CA31”of the frame FL3 as a retrieval key.

Here, it is presupposed that the switching device SWE3 has learned thecorrespondence relation between “CA31” and the port identifier {Pd[1] }to the address table FDB through past communications. Thus, theswitching device SWE3 acquires the port identifier {Pd[1] } anddecapsulates the frame FL3 to convert it to the frame FL2.

The switching device SWE3 transmits the decapsulated frame FL2 from theport (lower-link port) Pd[l] through the PB network 11 c to the switchSWB5 based on the retrieval result of the address table FDB. The switchSWB5 receives the frame FL2 and removes the service VLAN tag 16 from theframe FL2, thereby converting the frame FL2 into the frame FL1. Then,the switch SWB5 transmits the frame FL1 to the customer terminal TMhaving the customer address CMAC of “CA31” through the customer network12 e.

Note that, in the example of FIG. 1 and FIG. 2, the switching devicesSWE2 and SWE3 transmit or receive the frame FL2 to and from the PBnetworks 11 b and 11 c, but they can transmit or receive the frame FL1to and from the customer networks 12 c and 12 e according tocircumstances. More specifically, the edge switching device can generatethe frame FL3 by encapsulating the frame FL1 of FIG. 2 and can generatethe frame FL1 by decapsulating the frame FL3. Further, although theconfiguration example and the operation example based on the PBBstandard have been described here, they can be applied also to the EoE(Ethernet over Ethernet) standard in the same manner. An EoE frame isslightly different from the PBB frame (frame FL3) of FIG. 2 in a format,but it has substantially the same information as that of the PBB frameof FIG. 2.

<<Configuration of Relay System (Main Part)>>

FIG. 3 is a schematic diagram showing a configuration example around theMCLAG switch in the relay system of FIG. 1. As described above withreference to FIG. 1, the MCLAG switch MCLAGSW is made up of twoswitching devices (first and second switching devices) SWE1 a and SWE1b. In the same manner as the operation described with reference to FIG.1 and FIG. 2, the switching devices SWE1 a and SWE1 b convert anunencapsulated frame received from the outside (in this case, PB network11 a) of the PBB network 10 into an encapsulated frame and relay it tothe PBB network 10. Contrary to this, the switching devices SWE1 a andSWE1 b convert an encapsulated frame received from the PBB network 10into an unencapsulated frame and relay it to the outside (PB network 11a) of the PBB network. Further, the switching devices SWE1 a and SWE1 brelay an unencapsulated frame in the PB network 11 a and relay anencapsulated frame in the PBB network 10.

Each of the switching devices SWE1 a and SWE1 b has lower-link ports fortransmitting and receiving an unencapsulated frame and upper-link portsfor transmitting and receiving an encapsulated frame. As described abovewith reference to FIG. 1, the lower-link ports include the port Pd andthe MCLAG port (first MCLAG port) Pm1, and the upper-link ports includethe port Pu and the MCLAG port (second MCLAG port) Pm2. Furthermore, theupper-link ports include the bridge port Pb. More specifically, thebridge port PB belongs to the PEE network 10. The bridge ports Pbconnect one device and the peer device thereof through a communicationline 13. The communication line 13 is provided as, for example, anEthernet (registered trademark) line or provided as a dedicated line.

Also, in the example of FIG. 3, the network NWb1 of the PB network 11 ahas a switch SW1. The switch SW1 has LAG ports P1 and P2. The LAG portP1 is connected to the MCLAG port Pm1 of the switching device SWE1 athrough a communication line 14, and the LAG port P2 is connected to theMCLAG port Pm1 of the switching device SWE1 b through a communicationline 14. The communication line 14 is provided as, for example, anEthernet line. The switch SW1 sets MCLAG1 on the LAG ports P1 and P2. Inpractice, it is only necessary for the switch SW1 to set an ordinary LAGon the LAG ports P1 and P2, and there is no need for particularlydistinguishing the LAG and the MCLAG.

Similarly, the network NWbb of the PBB network 10 includes a core switchSWC. The core switch SWC has a LAG port P1 connected to the MCLAG portPm2 of the switching device SWE1 a and a LAG port P2 connected to theMCLAG port Pm2 of the switching device SWE1 b. The core switch SWC setsMCLAG2 (in practice, ordinary LAG) on the LAG ports P1 and P2.

Also, FIG. 3 shows customer terminals TM1 a, TM1 b and TM1 c andcustomer terminals TM2, TM3 and TM4. In the example of FIG. 1, thecustomer terminals TM1 a, TM1 b and TM1 c are included in the customernetworks 12 a and 12 b. The customer terminal TM2 is included in thecustomer networks 12 c and 12 d belonging to the lower link of theswitching device SWE2, and the customer terminal TM3 is included in thecustomer networks 12 e and 12 f belonging to the lower link of theswitching device SWE3. Also, the customer terminal TM4 is included inthe customer network (not shown) belonging to the lower link of theswitching device SWE4. In FIG. 3, as a matter of convenience,illustrations of the networks (NWc1 to NWc6) of each customer networkand the switches (SWB1 to SWB6) are omitted.

The customer terminal TM1 a is connected to the MCLAG ports (lower-linkports) Pm1 of the switching devices SWE1 a and SWE1 b via the switch SW1in the network NWb1. The customer terminal TM1 b is connected to theport (lower-link port) Pd of the switching device SWE1 a through thenetwork NWb1, and the customer terminal TM1 c is connected to the port(lower-link port) Pd of the switching device SWE1 b through the networkNWb1.

Also, the customer terminal TM3 is connected to the MCLAG ports(upper-link ports) Pm2 of the switching devices SWE1 a and SWE1 b viathe core switch SWC in the network NWbb. The customer terminal TM2 isconnected to the port (upper-link port) Pu of the switching device SWE1a through the network NWbb, and the customer terminal TM4 is connectedto the port (upper-link port) Pu of the switching device SWE1 b throughthe network NWbb.

In this configuration, FIG. 3 shows a method in which an active ACT or astandby SBY is set to MCLAG ports serving as member ports of each MCLAGas an example of an operation method of the MCLAG switch MCLAGSW. Inthis example, in the MCLAG1, the MCLAG port (first MCLAG port) Pm1 ofthe switching device SWE1 a is set to active ACT, and the MCLAG port Pm1of the switching device SWE1 b is set to standby SBY. Similarly, also inthe MCLAG2, the MCLAG port (second MCLAG port) Pm2 of the switchingdevice SWE1 a is set to active ACT, and the MCLAG port Pm2 of theswitching device SWE1 b is set to standby SBY.

When there is no fault, the MCLAG port set to active ACT is controlledto a transmission permitted state in which transmission is permitted. Inthis case, as an example thereof, the MCLAG port is controlled to atransmission/reception permitted state FW in which transmission andreception are both permitted. On the other hand, the MCLAG port set tostandby SBY is controlled to a transmission prohibited state in whichtransmission is prohibited. In this case, as an example thereof, theMCLAG port is controlled to a transmission prohibited state TBK in whichtransmission is prohibited and reception is permitted.

As a result, the frame from the MCLAG switch MCLAGSW to the switch SW1is always transmitted from the MCLAG port Pm1 of the switching deviceSWE1 a. Similarly, the frame from the MCLAG switch MCLAGSW to the coreswitch SWC is always transmitted from the MCLAG port Pm2 of theswitching device SWE1 a. On the other hand, the frame from the switchSW1 or the core switch SWC to the MCLAG switch MCLAGSW is transmittedfrom both of the LAG ports P1 and P2.

In this case, when a fault occurs at, for example, the MCLAG port Pm1 ofthe switching device SWE1 a, the switching operation in the occurrenceof fault is performed in the MCLAG switch MCLAGSW. Specifically, in theMCLAG1, the MCLAG port Pm1 of the switching device SWE1 b is controlledto the transmission/reception permitted state FW, and the MCLAG port Pm1of the switching device SWE1 a is controlled to, for example, atransmission/reception prohibited state in which transmission andreception are both prohibited.

Note that the operation method of the MCLAG switch MCLAGSW is notlimited to this method, and various methods can be used. For example, amethod in which MCLAG ports to transmit frames are equally distributedto the two switching devices SWE1 a and SWE1 b based on distribution IDand the like has been known.

Also, FIG. 3 shows a schematic configuration example of a main part ofthe switching devices SWE1 a and SWE1 b. In this case, each of theswitching devices SWE1 a and SWE1 b includes an address table FDB, aMCLAG table 21 and a relay processing unit 20. The relay processing unit20 mainly learns and retrieves the address table FDB.

The MCLAG table 21 retains one or a plurality of MCLAG ports inassociation with one or a plurality of MCLAG identifiers, respectively.In the case of FIG. 3, the MCLAG table 21 retains the MCLAG ports Pm1and Pm2 in association with MCLAG identifiers {MCLAG1} and {MCLAG2},respectively. Thus, each of the switching devices SWE1 a and SWE1 b setscommon MCLAG1 on its own MCLAG port Pm1 and the MCLAG port Pm1 of thepeer device, and sets common MCLAG2 on its own MCLAG port Pm2 and theMCLAG port Pm2 of the peer device.

The address table FDB retains the customer address present ahead of alower-link port in association with the port identifier representing thelower-link port or the MCLAG identifier corresponding to the lower-linkport. For example, the address table FDB of the switching device SWE2 ofFIG. 1 retains the customer address CMAC “CA21” present ahead of theport (lower-link port) Pd[1] in association with the port identifier{Pd[1] }. The address tables FDB of the switching devices SWE1 a andSWE1 b also retain the information similar to this.

Also, the address table FDB retains the customer address present aheadof the upper-link port in association with the encapsulation address andthe port identifier representing the upper-link port or the MCLAGidentifier corresponding to the upper-link port. For example, theaddress table FDB of the switching device SWE2 of FIG. 1 retains thecustomer address CMAC “CA31” present ahead of the port (upper-link port)Pu in association with the encapsulation address BMAC “BA3” and the portidentifier {Pu}. The address tables FDB of the switching devices SWE1 aand SWE1 b also retain the information similar to this.

The relay processing unit 20 includes a learning information controlunit 22 and a MCLAG identifier adding unit 23. When relaying the framereceived at the MCLAG port (for example, Pm1) to the bridge port Pb, theMCLAG identifier adding unit 23 adds a MCLAG identifier ({MCLAG1})corresponding to the MCLAG port to the frame. Though details thereofwill be described later, the learning information control unit 22controls the information learned to the address table FDB based onpredetermined conditions in order to prevent the unnecessary change ofthe learning contents of the address table.

<<Operation to be Premise of Relay System (Main Part) and Problem>>

FIG. 9 is an explanatory diagram showing an operation example in thecase where the relay system of FIG. 3 does not have the learninginformation control unit in the relay system studied as a premise of thepresent invention. In FIG. 9, it is presupposed that the customeraddresses (MAC addresses) CMAC of the customer terminals TM1 a, TM2 andTM3 are CA1 a, CA2 and CA3, respectively. Also, it is presupposed thatthe encapsulation addresses (MAC addresses) BMAC of the switchingdevices SWE1 a, SWE1 b, SWE2 and SWE3 are BA1 a, BA1 b, BA2 and BA3,respectively.

First, the case where a frame FL10 is transferred from the customerterminal TM1 a to the customer terminal TM2 is assumed. The switch SW1receives the frame (here, unencapsulated frame) FL10 and relays theframe FL10 to either of the LAG port P1 or P2 based on a predetermineddistribution rule. In this case, the frame FL10 is relayed to the LAGport P1.

The switching device SWE1 a receives the frame (here, unencapsulatedframe) FL10 at the MCLAG port Pm1. Then, the switching device SWE1 a(specifically, relay processing unit 20) learns the source customeraddress CSA “CA1 a” contained in the frame (unencapsulated frame) FL10in association with the port identifier of the port which has receivedthe frame (hereinafter, referred to as reception port identifier) to theaddress table FDB. In this case, the reception port identifier is theMCLAG identifier {MCLAG1}.

Also, it is presupposed that the switching device SWE1 a has learned thecorrespondence relation among the customer address CMAC “CA2”, theencapsulation address BMAC “BA2” and the port identifier {Pu} to theaddress table FDB through past communications. The switching device SWE1a (specifically, relay processing unit 20) retrieves the address tableFDB with using the destination customer address CDA “CA2” contained inthe frame (unencapsulated frame) FL10 as a retrieval key. The switchingdevice SWE1 a acquires the port identifier {Pu} of the port (upper-linkport) Pu as the port identifier of the destination (hereinafter,referred to as destination port identifier) based on the retrievalresult.

Then, the switching device SWE1 a encapsulates the frame (unencapsulatedframe) FL10 with the source encapsulation address BSA (its ownencapsulation address BMAC “BA1 a”) and the destination encapsulationaddress BDA (encapsulation address BMAC “BA2” based on address tableFDB). Then, the switching device SWE1 a transmits the frame (here,encapsulated frame) FL10 from the upper-link port Pu.

Next, the case where a frame FL11 is transferred from the customerterminal TM1 a to the customer terminal TM3 is assumed. The switch SW1receives the frame (here, unencapsulated frame) FL11 and relays theframe FL11 to either of the LAG port P1 or P2 based on a predetermineddistribution rule. In this case, the frame FL11 is relayed to the LAGport P2.

The switching device SWE1 b receives the frame (here, unencapsulatedframe) FL11 at the MCLAG port Pm1. Then, the switching device SWE1 b(specifically, relay processing unit 20) learns the source customeraddress CSA “CA1 a” contained in the frame (unencapsulated frame) FL11in association with the MCLAG identifier {MCLAG1} corresponding to thereception port identifier to the address table FDB.

Also, it is presupposed that the switching device SWE1 b has learned thecorrespondence relation among the customer address CMAC “CA3”, theencapsulation address BMAC “BA3” and the MCLAG identifier {MCLAG2} tothe address table FDB through past communications. The switching deviceSWE1 b (specifically, relay processing unit 20) retrieves the addresstable FDB with using the destination customer address CDA “CA3”contained in the frame (unencapsulated frame) FL11 as a retrieval key.As a result, the switching device SWE1 b acquires the MCLAG identifier{MCLAG2} as the destination port identifier.

Since the MCLAG port Pm2 of the switching device SWE1 b itself servingas a member port of the MCLAG2 is controlled to the transmissionprohibited state TBK, the switching device SWE1 b (specifically, relayprocessing unit 20) determines the port identifier {Pb} of the bridgeport Pb serving as the upper-link port as the transmission portidentifier of the frame FL11. In other words, the switching device SWE1b determines the bridge port Pb as the destination port.

In this case, the transmission port identifier means a port identifierof a port to actually transmit a frame. For example, when thedestination port identifier is not a MCLAG identifier but a normal portidentifier (for example, {Pu}), the transmission port identifier isequivalent to the destination port identifier. Meanwhile, when thedestination port identifier is a MCLAG identifier, the transmission portidentifier is the port identifier ({Pm2}) of the MCLAG port (forexample, Pm2) or the port identifier {Pb} of the bridge port Pb inaccordance with the control state of the MCLAG port.

In this case, the transmission port identifier is the port identifier{Pb} of the bridge port Pb serving as the upper-link port. Thus, theswitching device SWE1 b encapsulates the frame (unencapsulated frame)FL11 with the source encapsulation address BSA (its own encapsulationaddress BMAC “BA1 b”) and the destination encapsulation address BDA(encapsulation address BMAC “BA3” based on address table FDB).

Also, when relaying the frame received at the MCLAG port Pm1 to thebridge port Pb, the switching device SWE1 b (specifically, MCLAGidentifier adding unit 23) adds the MCLAG identifier {MCLAG1}corresponding to the reception port identifier SP to the frame. Thus,the switching device SWE1 b transmits the frame (here, encapsulatedframe) FL11, to which the MCLAG identifier {MCLAG1} has been added, fromthe bridge port Pb.

Meanwhile, the switching device SWE1 a receives the frame (encapsulatedframe) FL11 at the bridge port Pb. Then, the switching device SWE1 alearns the source customer address CSA “CA1 a” contained in the frame(encapsulated frame) FL11 in association with the source encapsulationaddress BSA “BA1 b” contained in the frame FL11 and the MCLAG identifier{MCLAG1} added to the frame FL11 to the address table FDB.

Also, it is presupposed that the switching device SWE1 a has learned thecorrespondence relation among the customer address CMAC “CA3”, theencapsulation address BMAC “BA3” and the MCLAG identifier {MCLAG2} tothe address table FDB through past communications. The switching deviceSWE1 a (specifically, relay processing unit 20) retrieves the addresstable FDB with using the destination encapsulation address BDA “BA3”contained in the frame (encapsulated frame) FL11 as a retrieval key. Asa result, the switching device SWE1 a acquires the MCLAG identifier{MCLAG2} as the destination port identifier.

Since the MCLAG port Pm2 of the switching device SWE1 a itself servingas a member port of the MCLAG2 is controlled to thetransmission/reception permitted state FW, the switching device SWE1 a(specifically, relay processing unit 20) determines the port identifier{Pm2} as the transmission port identifier of the frame FL11. In otherwords, the switching device SWE1 a determines the MCLAG port Pm2 as thedestination port. Thus, the switching device SWE1 a relays the frame(encapsulated frame) FL11 received at the bridge port Pb to the MCLAGport Pm2.

As described above, each of the switching devices (first and secondswitching devices) SWE1 a and SWE1 b generates an encapsulated frame byusing its own encapsulation address when relaying an unencapsulatedframe received at its own lower-link port to an upper-link port.Consequently, when the lower-link port which has received theunencapsulated frame is the MCLAG port (here, Pm1), each of theswitching devices SWE1 a and SWE1 b learns the source customer addresscontained in the unencapsulated frame in different two ways.

More specifically, there are the case where the learning of the addresstable FDB is performed based on the unencapsulated frame (FL10) and thecase where it is performed based on the encapsulated frame (FL11) likethe switching device SWE1 a of FIG. 9. In the former case, theencapsulation address is not learned, but in the latter case, theencapsulation address (here, BA1 b) is learned. For example, when theframe FL10 and the frame FL11 are alternately generated, the learningcontents of the address table FDB are frequently changed in spite ofbeing intended for the same customer address (here, CA1 a). Therefore,it is desired to prevent such an unstable situation.

Also, the switching device is sometimes provided with a function ofdetecting the frequent change of the learning contents intended for thesame customer address and regarding it as a fault. This function isintrinsically provided for detecting the occurrence of the loop path orthe like. On the other hand, since the phenomenon shown in FIG. 9normally does not correspond to the fault, it is desired to prevent theunnecessary fault detection resulting from it.

<<Operation of Relay System (Main Part) of Present Embodiment>>

FIG. 4 is an explanatory diagram showing an operation example of therelay system of FIG. 3. Like the above-described case of FIG. 9, FIG. 4shows the operation example in which the frame FL10 is transferred fromthe customer terminal TM1 a to the customer terminal TM2 and theoperation example in which the frame FL11 is transferred from thecustomer terminal TM1 a to the customer terminal TM3. The operation ofeach part with respect to the frame FL10 is the same as that of FIG. 9.

Meanwhile, with respect to the frame FL11, the switching device SWE1 areceives the frame (here, encapsulated frame) FL11, to which the MCLAGidentifier {MCLAG1} has been added, at the bridge port Pb like the caseof FIG. 9. At this time, the switching device SWE1 a learns the addresstable FDB by using the learning information control unit 22 unlike thecase of FIG. 9.

When the encapsulated frame to which the MCLAG identifier has been addedis received at the bridge port Pb (condition (A) and the encapsulationof the frame is performed by the peer device (condition (B)), thelearning information control unit 22 does not learn the sourceencapsulation address BSA contained in the encapsulated frame to theaddress table FDB. More specifically, the learning information controlunit 22 learns the source customer address CSA contained in theencapsulated frame in association with the MCLAG identifier added to theencapsulated frame to the address table FDB, but does not learn thesource encapsulation address BSA. Note that the learning informationcontrol unit 22 can determine whether the condition (B) is satisfied by,for example, determining whether the source encapsulation address BSAcontained in the encapsulated frame is the encapsulation address of thepeer device.

In the case of FIG. 4, the switching device SWE1 a receives theencapsulated frame (FL11), to which the MCLAG identifier {MCLAG1} hasbeen added, at the bridge port Pb. Further, the source encapsulationaddress BSA contained in the encapsulated frame (FL11) is theencapsulation address (BA1 b) of the peer device (SWE1 b). Therefore,since the above-described conditions (A) and (B) are both satisfied, thelearning information control unit 22 does not learn the encapsulationaddress (BA1 b) to the address table FDB. More specifically, thelearning information control unit 22 learns the source customer addressCSA “CA1 a” contained in the encapsulated frame (FL11) in associationwith the MCLAG identifier {MCLAG1} added to the frame to the addresstable FDB.

In this manner, the learning contents of the address table FDB in theswitching device SWE1 a become identical between the case where theunencapsulated frame (FL10) is received and the case where theencapsulated frame (FL11) is received. As a result, it becomes possibleto prevent the situation in which the learning contents of the addresstable FDB are unnecessarily changed described with reference to FIG. 9.Furthermore, it is also possible to prevent the unnecessary faultdetection described with reference to FIG. 9.

Note that the problem described with reference to FIG. 9 may occur notonly in the case of supposing the frame transfer path shown in FIG. 9but also in the case of supposing the other transfer path. In theexample of FIG. 4, the switch SW1 selects the LAG port by the hashoperation using the source customer address CSA and the destinationcustomer address CDA. In this case, the switch SW1 selects the same LAGport if the source and destination customer addresses CSA and CDA areidentical to each other.

Here, for example, the case where a customer terminal (defined as TM3′)different from the customer terminal TM3 is connected to the lower linkof the switching device SW3 of FIG. 4 and a frame is transferred fromthe customer terminal TM1 a to the customer terminal (TM3′) instead ofthe frame FL10 is assumed. In this case, since the frame is differentfrom the frame FL11 in the destination customer address CDA, the switchSW1 selects the LAG port P1 in some cases. Thus, the problem similar tothat of FIG. 9 occurs.

Further, depending on the distribution rule of LAG, even when the sourceand destination customer addresses CSA and CDA are identical to eachother, the LAG ports to be selected are arbitrarily distributed for eachframe in some cases. In such a case, in the frame transfer from thecustomer terminal TM1 a to the customer terminal TM3, the same problemmay occur when the switch SW1 equally distributes the LAG ports P1 andP2 to transmit the frame. Also, in the case of the switch SW1 like this,the same problem may occur also in the frame transfer from the customerterminal TM1 a to the customer terminal TM2 and in the frame transferfrom the customer terminal TM1 a to the customer terminal TM1 b.

As described above, essentially, the problem described with reference toFIG. 9 may occur when the lower-link ports of the switching devices SWE1a and SWE1 b include the MCLAG port. More specifically, the upper-linkports may be the MCLAG port (for example, Pm2) or the port on whichMCLAG is not set (for example, Pu), and the lower-link ports do not haveto include the port on which MCLAG is not set (for example, Pb).

However, in particular, when the operation method of the MCLAG shown inFIG. 3 and others (namely, method in which active and standby are set toMCLAG ports) is used, the problem described with reference to FIG. 9 ismore likely to occur. Specifically, when relaying the frame received atthe MCLAG1 to the MCLAG2, since the MCLAG port to which the frame isrelayed is fixedly determined, the communication of the encapsulatedframes via the bridge ports Pb is performed frequently. As a result, theproblem described with reference to FIG. 9 is likely to occur. Thus, insuch a case, the application of the method described with reference toFIG. 4 and others is particularly beneficial.

Also, the learning information control unit 22 can determine theconditions (A) and (B) by various ways other than the example describedabove. For example, the learning information control unit 22 candetermine whether the condition (B) is satisfied by determining whetherthe MCLAG identifier added to the encapsulated frame is the MCLAGidentifier of the MCLAG port serving as the lower-link port. When theMCLAG identifier of the lower-link port is added, it means that theencapsulation of the frame is performed by the peer device.

FIG. 5 is an explanatory diagram showing another operation example ofthe relay system of FIG. 3. FIG. 5 shows an operation example in which aframe is transferred from the customer terminal TM3 to the customerterminal TM1 a contrary to the case of FIG. 4. An unencapsulated frametransmitted from the customer terminal TM3 is converted into anencapsulated frame in the switching device SWE3. At this time, theswitching device SWE3 generates the encapsulated frame containing thesource encapsulation address BSA “BA3” and the destination encapsulationaddress BDA “BA1 b” based on the learning information of the addresstable by the frame FL11 of FIG. 4.

The core switch SWC receives the encapsulated frame and relays theencapsulated frame to either of the LAG port P1 or P2 based on apredetermined distribution rule. In FIG. 5, the frame relayed to the LAGport P1 is denoted by FL15, and the frame relayed to the LAG port P2 isdenoted by FL16. The switching device SWE1 a receives the frame(encapsulated frame) FL15 at the MCLAG port Pm2. Then, the switchingdevice SWE1 a (specifically, relay processing unit 20) learns the sourcecustomer address CSA “CA3” of the frame FL15 in association with thesource encapsulation address BSA “BA3” and the MCLAG identifier {MCLAG}corresponding to the reception port identifier to the address table FDB.

Here, each of the switching devices SWE1 a and SWE1 b has a function ofretrieving its own address table FDB with using the destination customeraddress CDA contained in the received encapsulated frame as a retrievalkey when the destination encapsulation address BDA contained in theframe is its own encapsulation address or the encapsulation address ofthe peer device. In this case, since the destination encapsulationaddress BDA “BA1 b” of the frame FL15 is the encapsulation address ofthe peer device, the switching device SWE1 a (specifically, relayprocessing unit 20) retrieves the address table FDB with using thedestination customer address CDA “CA1 a” as a retrieval key.

The address table FDB of the switching device SWE1 a retains thecorrespondence relation between the customer address CMAC “CA1 a” andthe MCLAG identifier {MCLAG1} by the operation described with referenceto FIG. 4. Therefore, as a result of the retrieval of the address tableFDB, the switching device SWE1 a acquires the MCLAG identifier {MCLAG1}.Further, since the MCLAG port Pm1 of the switching device SWE1 a itselfserving as a member port of the MCLAG1 is controlled to thetransmission/reception permitted state FW, the switching device SWE1 a(specifically, relay processing unit 20) determines the port identifier{Pm1} as the transmission port identifier. In other words, the switchingdevice SWE1 a determines its own MCLAG port Pm1 as the destination port.Since the destination port is the lower-link port, the switching deviceSWE1 a converts the received frame (encapsulated frame) FL15 into anunencapsulated frame and then relays it to the MCLAG port Pm1.

On the other hand, the switching device SWE1 b receives the frame(encapsulated frame) FL16 at the MCLAG port Pm2. Then, the switchingdevice SWE1 b (specifically, relay processing unit 20) learns the sourcecustomer address CSA “CA3” of the frame FL16 in association with thesource encapsulation address BSA “BA3” and the MCLAG identifier {MCLAG2}corresponding to the reception port identifier to the address table FDB.Also, since the destination encapsulation address BDA “BA1 b” of theframe FL16 is the encapsulation address of the switching device SWE1 bitself, the switching device SWE1 b (specifically, relay processing unit20) retrieves the address table FDB with using the destination customeraddress CDA “CA1 a” as a retrieval key.

The address table FDB of the switching device SWE1 b retains thecorrespondence relation between the customer address CMAC “CA1 a” andthe MCLAG identifier {MCLAG} by the operation described with referenceto FIG. 4. Therefore, as a result of the retrieval of the address tableFDB, the switching device SWE1 b acquires the MCLAG identifier {MCLAG1}.Further, since the MCLAG port Pm1 of the switching device SWE1 b itselfserving as a member port of the MCLAG1 is controlled to the transmissionprohibited state TBK, the switching device SWE1 b (specifically, relayprocessing unit 20) determines the bridge port Pb as the destinationport.

Since the destination port is the upper-link port, the switching deviceSWE1 b relays the received frame (encapsulated frame) FL16 as it is(without decapsulation) to the bridge port Pb. At this time, theswitching device SWE1 b (specifically, MCLAG identifier adding unit 23)adds the MCLAG identifier {MCLAG2} corresponding to the reception portidentifier SP to the frame FL16.

The switching device SWE1 a receives the frame (encapsulated frame)FL16, to which the MCLAG identifier {MCLAG2} has been added, at thebridge port Pb. In this case, unlike the case of FIG. 4, since thesource encapsulation address BSA “BA3” is not the encapsulation addressof the peer device, the switching device SWE1 a (specifically, learninginformation control unit 22) learns the source encapsulation addressBSA. More specifically, the switching device SWE1 a (learninginformation control unit 22) learns the source customer address CSA“CA3” contained in the frame FL16 in association with the sourceencapsulation address BSA “BA3” and the MCLAG identifier {MCLAG2} addedto the frame FL16 to the address table FDB.

Also, since the destination encapsulation address BDA “BA1 b” of theframe FL16 is the encapsulation address of the peer device, theswitching device SWE1 a (specifically, relay processing unit 20)retrieves the address table FDB with using the destination customeraddress CDA “CA1 a” as a retrieval key. As a result, like the case ofthe frame FL15, the switching device SWE1 a acquires the MCLAGidentifier {MCLAG} and then relays the frame (unencapsulated frame) FL16to the MCLAG port Pm1 through the same process as that of the frameFL15.

<<Details of Switching Device>>

FIG. 6 is a block diagram showing a configuration example of the mainpart of the switching device constituting the MCLAG switch in the relaysystem of FIG. 3. FIG. 7 is a schematic diagram showing a configurationexample of the address table in FIG. 6. FIG. 8A is a schematic diagramshowing a configuration example of the reception-side IVID managementtable in FIG. 6, FIG. 8B is a schematic diagram showing a configurationexample of the transmission-side IVID management table in FIG. 6, andFIG. 8C is a schematic diagram showing a configuration example of theMCLAG table in FIG. 6.

The switching device SWE shown in FIG. 6 includes lower-link portsconnected to the outside of the PBB network 10 (for example, PB network11), upper-link ports connected to the PBB network 10, variousprocessing units and various tables. The lower-link ports include atleast a MCLAG port and include the MCLAG port Pm1 and the port Pd onwhich MCLAG is not set in the example of FIG. 6. The upper-link portsinclude the bridge port Pb and a port which is indifferent about whetherthe MCLAG is set and include the MCLAG port Pm2 and the port Pu on whichthe MCLAG is not set in the example of FIG. 6. Hereinafter, variousprocessing units and tables will be described.

An interface unit 30 includes a reception buffer and a transmissionbuffer, transmits or receives an unencapsulated frame to or from thelower-link ports (Pd, Pm1), and transmits or receives an encapsulatedframe to or from the upper-link ports (Pm2, Pu, Pb). Further, theinterface unit 30 includes a fault detecting unit 38 and a receptionport identifier adding unit 39. When a frame is received at any of theplurality of ports, the reception port identifier adding unit 39 adds areception port identifier to the frame.

The fault detecting unit 38 detects presence or absence of fault(presence or absence of link down) for each of the plurality of ports byhardware. For example, the fault detecting unit 38 monitors a receivedoptical signal level and detects the presence of link down when anabnormal state such as the insufficiency of the optical signal levelcontinues for a predetermined period. Alternatively, the fault detectingunit 38 monitors the presence or absence of link pulse signal generatedin an idle state and the presence or absence of data signal in anon-idle state based on received signals, and detects the presence oflink down when an abnormal state such as the absence of both of linkpulse signal and data signal continues for a predetermined period.

An IVID assigning unit 31 assigns an internal VLAN identifier IVID to anunencapsulated frame received at the lower-link port or an encapsulatedframe received at the upper-link port based on a reception-side IVIDmanagement table 32 a determined in advance by a service provider or thelike. As shown in FIG. 8A, the reception-side IVID management table 32 aretains the combination of the service VLAN identifier SVID and thereception port identifier in association with the internal VLANidentifier IVID.

The service VLAN identifier SVID is contained in an unencapsulatedframe, and the reception port identifier is added to the unencapsulatedframe by the reception port identifier adding unit 39. The IVIDassigning unit 31 acquires the internal VLAN identifier IVIDcorresponding to the service VLAN identifier SVID and the reception portidentifier from the reception-side IVID management table 32 a, and addsthe internal VLAN identifier IVID to an unencapsulated frame to transmitit to the relay processing unit 20.

Also, as shown in FIG. 8A, the reception-side IVID management table 32 aretains the combination of the backbone VLAN identifier BVID and thereception port identifier in association with the internal VLANidentifier IVID. The backbone VLAN identifier BVID is contained in anencapsulated frame, and the reception port identifier is added to theencapsulated frame by the reception port identifier adding unit 39. TheIVID assigning unit 31 acquires the internal VLAN identifier IVIDcorresponding to the backbone VLAN identifier BVID and the receptionport identifier from the reception-side IVID management table 32 a, andadds the internal VLAN identifier IVID to an encapsulated frame totransmit it to the relay processing unit 20.

As shown in FIG. 8C, the MCLAG table 21 retains one or a plurality ofMCLAG ports in association with one or a plurality of MCLAG identifiers,respectively. Further, in this example, the MCLAG table 21 retains alsoa control state of each MCLAG port. In the example of FIG. 8C, the portidentifier {Pm1} representing the MCLAG port Pm1 is associated with theMCLAG identifier {MCLAG1} and is controlled to thetransmission/reception permitted state FW. Also, the port identifier{Pm2} representing the MCLAG port Pm2 is associated with the MCLAGidentifier {MCLAG2} and is controlled to the transmission/receptionpermitted state FW.

As shown in FIG. 7, the address table FDB retains the customer addresspresent ahead of a lower-link port in association with the portidentifier representing the lower-link port or the MCLAG identifiercorresponding to the lower-link port and the internal VLAN identifierIVID. Also, the address table FDB retains the customer address presentahead of an upper-link port in association with the encapsulationaddress, the port identifier representing the upper-link port or theMCLAG identifier corresponding to the upper-link port and the internalVLAN identifier IVID.

FIG. 7 shows the address table FDB of the switching device SWE1 a ofFIG. 4 as an example. The customer address which is not described inFIG. 4 will be described here. Customer addresses CA1 b, CA1 c and CA4in FIG. 7 are MAC addresses of the customer terminals TM1 b, TM1 c andTM4 in FIG. 4, respectively. Also, an encapsulation address BA4 in FIG.7 is a MAC address of the switching device SWE4 in FIG. 4. In theaddress table FDB, for example, these customer addresses CA1 b, CA1 cand CA4 are retained in the states described below.

The customer address CA1 b present ahead of the port (lower-link port)Pd is retained in association with the port identifier {Pd} and theinternal VLAN identifier IVID “xxx”. Also, the customer address CA1 cpresent ahead of the bridge port (upper-link port) Pb is retained inassociation with the encapsulation address BMAC “BA1 b”, the portidentifier {Pb} and the internal VLAN identifier IVID “xxx”. Further,the customer address CA4 present ahead of the bridge port (upper-linkport) Pb is retained in association with the encapsulation address BMAC“BA4”, the port identifier {Pb} and the internal VLAN identifier IVID“xxx”.

For example, the MCLAG control unit 33 controls the operation of theMCLAG switch MCLAGSW by transmitting and receiving various controlframes. One example of the control frames is a MCLAG control frame forperforming the transmission and reception to and from a peer device atregular intervals via bridge ports Pb. By the transmission and thereception of the MCLAG control frame, the fault information can beshared between the respective switching devices and the living of therespective switching devices can be confirmed.

Also, as another example, the control frames may include a control framesuch as Ethernet OAM (Operations, Administration, and Maintenance). Inthe Ethernet OAM, for example, the continuity with an outside df thedevice can be monitored by transmitting and receiving a control frame(test frame) referred to as CCM (Continuity Check Message) or the likeat regular intervals. In this manner, for example, the presence orabsence of fault at the MCLAG ports Pm1 and Pmt can be detected.

The MCLAG control unit 33 determines the control state of each MCLAGport in the MCLAG table 21 based on the fault information from the faultdetecting unit 38, the fault information acquired from a MCLAG controlframe or CCM, and setting information of active ACT and standby SBYdetermined in advance. Specifically, when the MCLAG port of its owndevice has a fault, the MCLAG control unit 33 controls the MCLAG port tothe transmission/reception prohibited state.

Also, when the MCLAG port of its own device has no fault and is set tothe active ACT, the MCLAG control unit 33 controls the MCLAG port to thetransmission/reception permitted state FW. Further, when the MCLAG portof its own device has no fault and is set to the standby SBY, the MCLAGcontrol unit 33 controls the MCLAG port of its own device in accordancewith the presence or absence of fault at the MCLAG port on an active ACTside.

Specifically, when the MCLAG port on the active ACT side has no fault,the MCLAG control unit 33 controls the MCLAG port of its own device tothe transmission prohibited state TBK, and when the MCLAG port on theactive ACT side has a fault, the MCLAG control unit 33 controls theMCLAG port of its own device to the transmission/reception permittedstate FW. The information of the presence or absence of fault at theMCLAG port on the active ACT side can be acquired by the MCLAG controlframe described above.

The relay processing unit 20 includes the learning information controlunit 22 and the MCLAG identifier adding unit 23, and performs thelearning and retrieval of the address table FDB when receiving a frameat a port as described with reference to FIG. 4, FIG. 5, FIG. 9 andothers. Specifically, when receiving a frame at a port, the relayprocessing unit 20 learns various kinds of information shown in FIG. 7to the address table FDB in accordance with whether the frame is anunencapsulated frame or an encapsulated frame. In addition, when theframe is an encapsulated frame, the operation by the learninginformation control unit 22 is also performed as described withreference to FIG. 4 and FIG. 5.

In the address table FDB of FIG. 7, the internal VLAN identifier IVID isdetermined by the IVID assigning unit 31. The port identifier in theport ID/MCLAG ID is determined by the reception port identifier addingunit 39. The MCLAG identifier in the port ID/MCLAG ID is determined withreference to the MCLAG table 21 based on the reception port identifieradded by the reception port identifier adding unit 39. Also, whenreceiving a frame to which a MCLAG identifier is added from the peerdevice, the MCLAG identifier in the port ID/MCLAG ID is determined to bethe MCLAG identifier.

Also, when receiving an unencapsulated frame, the relay processing unit20 retrieves the address table FDB with using the destination customeraddress CDA contained in the frame and the internal VLAN identifier IVIDadded to the frame as retrieval keys, thereby acquiring the destinationport identifier and the destination encapsulation address BDA. On theother hand, when receiving an encapsulated frame, the relay processingunit 20 performs the following processes in accordance with thedestination encapsulation address BDA contained in the frame.

First, when the destination encapsulation address BDA is theencapsulation address of its own device or the peer device, the relayprocessing unit 20 retrieves the address table FDB with using thedestination customer address CDA contained in the frame and the internalVLAN identifier IVID added to the frame as retrieval keys, therebyacquiring the destination port identifier. The encapsulation address ofthe peer device is retained in a peer device address retaining unit 34in advance. On the other hand, when the destination encapsulationaddress BDA is not the encapsulation address of its own device or thepeer device, the relay processing unit 20 retrieves the address tableFDB with using the destination encapsulation address BDA contained inthe frame and the internal VLAN identifier IVID added to the frame asretrieval keys, thereby acquiring the destination port identifier.

Then, when the destination port identifier acquired in theabove-described manner is not the MCLAG identifier but the normal portidentifier, the relay processing unit 20 determines the destination portidentifier as the transmission port identifier. On the other hand, whenthe destination port identifier is the MCLAG identifier, the relayprocessing unit 20 determines the control state of the MCLAG port of itsown device serving as a member port of the MCLAG identifier based on theMCLAG table 21. When the control state of the MCLAG port of its owndevice is the transmission/reception permitted state FW, the relayprocessing unit 20 determines the port identifier of the MCLAG port asthe transmission port identifier, and when the control state is thetransmission prohibited state TBK, the relay processing unit 20determines the port identifier {Pb} of the bridge port Pb as thetransmission port identifier.

The relay processing unit 20 adds the transmission port identifierdetermined in the above-described manner to the frame. At this time,when the reception port identifier is the MCLAG identifier, the MCLAGidentifier adding unit 23 further adds the MCLAG identifier to theframe. Then, the relay processing unit 20 transmits the frame to adifferent processing unit in accordance with the correspondence relationbetween the reception port identifier and the transmission portidentifier.

Specifically, when the reception port identifier is the lower-link portand the transmission port identifier is the upper-link port, the relayprocessing unit 20 transmits an unencapsulated frame to an encapsulationexecuting unit 35. Also, when the reception port identifier is theupper-link port and the transmission port identifier is the lower-linkport, the relay processing unit 20 transmits an encapsulated frame to adecapsulation executing unit 36. Further, when both of the receptionport identifier and the transmission port identifier are the lower-linkports or the upper-link ports, the relay processing unit 20 transmits aframe to a relay executing unit 37.

The encapsulation executing unit 35 converts the received unencapsulatedframe into an encapsulated frame. At this time, the encapsulationexecuting unit 35 determines an encapsulation address of its own deviceas the source encapsulation address BSA, and determines the destinationencapsulation address BDA acquired by the relay processing unit 20 asthe destination encapsulation address BDA. Furthermore, theencapsulation executing unit 35 determines the service instanceidentifier ISID and the backbone VLAN identifier BVID based on atransmission-side IVID management table 32 b determined in advance by aservice provider or the like.

As shown in FIG. 8B, the transmission-side IVID management table 32 bretains the combination of the internal VLAN identifier IVID and thetransmission port identifier in association with the service instanceidentifier ISID and the backbone VLAN identifier BVID. The internal VLANidentifier IVID is added to the unencapsulated frame by the IVIDassigning unit 31, and the transmission port identifier is added to theframe by the relay processing unit 20. Based on this, the encapsulationexecuting unit 35 generates an encapsulated frame containing the serviceinstance identifier ISID and the backbone VLAN identifier BVID, andtransmits it to the relay executing unit 37.

The decapsulation executing unit 36 converts the received encapsulatedframe into an unencapsulated frame. At this time, the decapsulationexecuting unit 36 determines the service VLAN identifier SVID based onthe transmission-side IVID management table 32 b. As shown in FIG. 8B,the transmission-side IVID management table 32 b retains the combinationof the internal VLAN identifier IVID and the transmission portidentifier in association with the service VLAN identifier SVID otherthan the information described above. Based on this, the decapsulationexecuting unit 36 generates an unencapsulated frame containing theservice VLAN identifier SVID, and transmits it to the relay executingunit 37.

The relay executing unit 37 transmits the above-described frames fromeach of the processing units (unencapsulated frame and encapsulatedframe) to a predetermined transmission buffer in the interface unit 30.The predetermined transmission buffer corresponds to the transmissionport identifier added to the frame. At this time, the relay executingunit 37 deletes the unnecessary information added to the frame (forexample, internal VLAN identifier IVID and transmission portidentifier). The transmission buffer in the interface unit 30 receivesthe frame from the relay executing unit 37, and transmits the frame to acorresponding port (that is, lower-link port or upper-link portcorresponding to transmission port identifier).

As described above, by using the relay system and switching device ofthe present embodiment, typically, it becomes possible to prevent thesituation in which the learning contents of the address table areunnecessarily changed. Note that the configuration example in which theconversion between the service VLAN identifier SVID and the serviceinstance identifier ISID and backbone VLAN identifier BVID is performedvia the internal VLAN identifier IVID has been described with referenceto FIG. 6, but the configuration in which the conversion therebetween isperformed without the internal VLAN identifier IVID can be used. Forexample, it is also possible to determine the correspondence relationbetween the service VLAN identifier SVID and the service instanceidentifier ISID and backbone VLAN identifier BVID in a table and performthe conversion by using the table. In this case, the backbone VLANidentifier BVID needs to be learned to the address table FDB instead ofthe internal VLAN identifier IVID.

In the foregoing, the invention made by the inventor of the presentinvention has been concretely described based on the embodiments.However, it is needless to say that the present invention is not limitedto the foregoing embodiments and various modifications and alterationscan be made within the scope of the present invention. For example, theembodiments above have been described in detail so as to make thepresent invention easily understood, and the present invention is notlimited to the embodiment having all of the described constituentelements. Also, a part of the configuration of one embodiment may bereplaced with the configuration of another embodiment, and theconfiguration of one embodiment may be added to the configuration ofanother embodiment. Furthermore, another configuration may be added to apart of the configuration of each embodiment, and a part of theconfiguration of each embodiment may be eliminated or replaced withanother configuration.

What is claimed is:
 1. A relay system comprising: a first switchingdevice and a second switching device which are disposed at entrance orexit of a Provider Backbone Bridge (PBB) network in which relaying basedon a PBB standard is performed, the first and second switching devicesconverting an unencapsulated frame received from outside of the PBBnetwork into an encapsulated frame and relaying the encapsulated frameto the PBB network, and the first and second switching devicesconverting the encapsulated frame received from the PBB network into theunencapsulated frame and relaying the unencapsulated frame to theoutside of the PBB network, wherein the unencapsulated frame contains acustomer address, the encapsulated frame has a configuration in which anencapsulation address is added to the unencapsulated frame based on thePBB standard, each of the first switching device and the secondswitching device includes: a lower-link port which transmits or receivesthe unencapsulated frame; an upper-link port which transmits or receivesthe encapsulated frame; one or a plurality of multi-chassis linkaggregation group (MCLAG) ports which include a first MCLAG port servingas the lower-link port and on which an inter-device LAG is set; a bridgeport which serves as the upper-link port and connects one device and apeer device; an address table which retains the customer address presentahead of the lower-link port in association with a port identifierrepresenting the lower-link port or a MCLAG identifier corresponding tothe lower-link port and retains the customer address present ahead ofthe upper-link port in association with the encapsulation address and aport identifier representing the upper-link port or a MCLAG identifiercorresponding to the upper-link port; and a relay processing unit,comprising a processor, which learns and retrieves the address table,and the processor is configured to: when a frame received at the MCLAGport is relayed to the bridge port, add a MCLAG identifier correspondingto the MCLAG port to the frame; when the encapsulated frame to which theMCLAG identifier has been added is received at the bridge port andencapsulation of the frame is performed by the peer device, learn asource customer address contained in the encapsulated frame inassociation with the MCLAG identifier added to the encapsulated frame tothe address table, and not learn the encapsulation address contained inthe encapsulated frame to the address table; and determine whether asource encapsulation address contained in the encapsulated frame is theencapsulation address of the peer device, thereby determining whetherthe encapsulation of the frame is performed by the peer device.
 2. Therelay system according to claim 1, wherein, when each of the firstswitching device and the second switching device relays theunencapsulated frame received at its own first MCLAG port to theupper-link port, each of the first switching device and the secondswitching device generates the encapsulated frame by using its ownencapsulation address.
 3. The relay system according to claim 1, whereinone of the first MCLAG ports of the first switching device and thesecond switching device is set to a transmission permitted state and theother thereof is set to a transmission prohibited state in advance, andwhen relaying a frame to the MCLAG port based on a retrieval result ofthe address table, the processor is configured to relay the frame to theMCLAG port of its own device when the MCLAG port of its own device is inthe transmission permitted state, and relay the frame to the bridge portwhen the MCLAG port of its own device is in the transmission prohibitedstate.
 4. The relay system according to claim 3, wherein the one orplurality of MCLAG ports further include a second MCLAG port serving asthe upper-link port.
 5. The relay system according to claim 1, wherein,when a destination encapsulation address contained in the receivedencapsulated frame is the encapsulation address of its own device or thepeer device, the processor is configured to retrieve an address table ofits own device with using a destination customer address contained inthe encapsulated frame as a retrieval key.
 6. A switching device whichis disposed at entrance or exit of a Provider Backbone Bridge (PBB)network in which relaying based on a PBB standard is performed, theswitching device converting an unencapsulated frame received fromoutside of the PBB network into an encapsulated frame and relaying theencapsulated frame to the PBB network, and the switching deviceconverting the encapsulated frame received from the PBB network into theunencapsulated frame and relaying the unencapsulated frame to theoutside of the PBB network, wherein the unencapsulated frame contains acustomer address, the encapsulated frame has a configuration in which anencapsulation address is added to the unencapsulated frame based on thePBB standard, the switching device further includes: a lower-link portwhich transmits or receives the unencapsulated frame; an upper-link portwhich transmits or receives the encapsulated frame; one or a pluralityof multi-chassis link aggregation group (MCLAG) ports which include afirst MCLAG port serving as the lower-link port and on which aninter-device LAG is set; a bridge port which serves as the upper-linkport and connects one device and a peer device; an address table whichretains the customer address present ahead of the lower-link port inassociation with a port identifier representing the lower-link port or aMCLAG identifier corresponding to the lower-link port and retains thecustomer address present ahead of the upper-link port in associationwith the encapsulation address and a port identifier representing theupper-link port or a MCLAG identifier corresponding to the upper-linkport; and a relay processing unit, comprising a processor, which learnsand retrieves the address table, and the processor is configured to:when a frame received at the MCLAG port is relayed to the bridge port,add a MCLAG identifier corresponding to the MCLAG port to the frame;when the encapsulated frame to which the MCLAG identifier has been addedis received at the bridge port and encapsulation of the frame isperformed by the peer device, learn a source customer address containedin the encapsulated frame in association with the MCLAG identifier addedto the encapsulated frame to the address table, and not learn theencapsulation address contained in the encapsulated frame to the addresstable; and determine whether a source encapsulation address contained inthe encapsulated frame is the encapsulation address of the peer device,thereby determining whether the encapsulation of the frame is performedby the peer device.
 7. The switching device according to claim 6,wherein, when the switching device relays the unencapsulated framereceived at the first MCLAG port to the upper-link port, the switchingdevice generates the encapsulated frame by using its own encapsulationaddress.
 8. The switching device according to claim 6, wherein one ofthe first MCLAG ports of the switching device and the peer device is setto a transmission permitted state and the other thereof is set to atransmission prohibited state in advance, and when relaying a frame tothe MCLAG port based on a retrieval result of the address table, theprocessor is configured to relay the frame to the MCLAG port of its owndevice when the MCLAG port of its own device is in the transmissionpermitted state, and relay the frame to the bridge port when the MCLAGport of its own device is in the transmission prohibited state.
 9. Theswitching device according to claim 8, wherein the one or plurality ofMCLAG ports further include a second MCLAG port serving as theupper-link port.
 10. The switching device according to claim 6, wherein,when a destination encapsulation address contained in the receivedencapsulated frame is the encapsulation address of its own device or thepeer device, the processor is configured to retrieve an address table ofits own device with using a destination customer address contained inthe encapsulated frame as a retrieval key.